Use of sinusoidal voltages with fixed frequency in the preparation of tyrosinase based electrochemical biosensors for dopamine electroanalysis

Sinusoidal voltages (SV) of fixed frequency were used in the preparation of electrochemical biosensors based on gold (Au) disk microelectrode arrays (MEAs) modified with a bio-composite material consisting of poly(3,4-ethylenedioxythiophene) conducting polymer (PEDOT) and tyrosinase (Tyr). The SV was applied over a d.c. potential of 0.60 V vs. Ag/AgCl/KCl (3 M) in order to assess the contribution of the sinusoidal signal to the electrochemical polymerization of the monomer. The use of SV with fixed frequency ensured the preparation of bio-composite materials with given properties. A high porosity is expected, as the Tyr enzyme is entrapped within the polymeric layer by electrostatic interactions during the electrochemical polymerization process. The morphology and the chemical nature of the prepared coatings were studied by scanning electron microscopy, optical profilometry, and infrared reflection absorption spectroscopy. The MEA devices present two independent arrays separated by an insulating gap. One electrode from the device was modified by a PEDOT-Tyr layer, while the second electrode was modified with a PEDOT layer. The analytical determination of dopamine and hydroquinone was carried out via bipotentiostatic measurements by simultaneous polarization of both PEDOT-Tyr and PEDOT modified electrodes from one device using cyclic voltammetry. The analytical performance in terms of linear range, detection and quantification limits, sensitivity, repeatability, re-usability and operational stability, have been assessed. The PEDOT-Tyr based biosensor, prepared at 0.60 V d.c. potential value and SV signal with 50 mHz frequency and ±350 mV amplitude, exhibited a low detection limit of 2.4 × 10−7 M dopamine, an excellent repeatability of 4.1%, and a recovery of 100.2% were achieved for dopamine determination. The proposed biosensor was also successfully applied in dopamine electroanalysis in pharmaceutical products.